Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. In recognition of these expenses, added emphasis has been placed on efficiencies associated with well completions and maintenance over the life of the well. Over the years, ever increasing well depths and sophisticated architecture have made reductions in time and effort spent in completions and maintenance operations of even greater focus.
In terms of architecture, a well often includes a variety of lateral legs emerging from a main bore. For example, the terminal end of a cased well often extends into an open-hole region branching out into multiple lateral legs providing reservoir access. Of course, such open-hole lateral legs are also often found extending from other regions of the main bore as well. This type of architecture may enhance access to the reservoir, for example, where the reservoir is substantially compartmentalized. Regardless, such open-hole lateral leg sections often present their own particular challenges when it comes to completions installation and maintenance.
In many circumstances, the mere creation of the multilateral architecture presents stability issues. That is, once the main bore is formed, and generally cased, the noted variety of lateral legs are sequentially drilled into the formation, emerging from the bore. This results in exposure of the main bore to an emerging open network of legs connected thereto without any fluid or pressure control. This may be of consequence where the nature of the well architecture is such that fluid access is more readily attained, for example, without the need for prior stimulation. That is to say, depending on the nature of the architecture relative the reservoir, the mere process of completing the well and installing hardware may result in fluid losses well in advance of intended production.
In order to avoid such fluid loss interference and allow completions operations to continue, comparatively heavy solid particle fluids may be pumped into the well. Unfortunately, this manner of killing fluid loss or production has significant drawbacks. That is, aside from the operational time lost to the kill application, once installation is completed, follow-on applications dedicated to regaining reservoir access must be undertaken. These applications require more time and resources devoted to the introduction of stimulation and recovery fluids, namely directed at removal of the heavier kill fluids. Overall, the time lost to killing and restoring the well for sake of multilateral completions may be in the neighborhood of days to weeks at a cost of several hundred thousand dollars.
Once more, complete revival of the well following the kill is unlikely. That is, even following well restoration or clean-out applications, the overall efficiency and productivity of the well will remain compromised to a degree as a result of having undertaking the kill application. This is due to the fact that complete removal of the kill fluid is impractical. Indeed, in the multilateral situation, it is quite likely that production from one or more of the multilateral legs will remain closed off even after well restoration. Nevertheless, in the case of multilateral completions prone to fluid losses during installation, operators are left with only the options of utilizing the noted kill techniques or limiting the overall sophistication of the multilateral in terms of depth and number of open legs.